The invention relates to the general field of magnetic disk systems with particular reference to forming step P1.
Read-write heads for magnetic disk systems have undergone substantial development during the last few years. In particular, older systems in which a single device was used for both reading and writing, have given way to configurations in which the two functions are performed by different structures that have been integrated into a single unit. In FIG. 1 we show a schematic representation of a write head of a type currently under development in our laboratories. The magnetic field that xe2x80x98writesxe2x80x99 a bit at the surface of recording medium 18 (generally referred to as the air bearing surface or ABS) is generated by a flat coil, whose windings, such as 16, can be seen in the figure. The magnetic flux generated by the flat coil is largely confined to the pole pieces. These comprise the upper pole pieces 12 and 13 (known as P2 and P3 respectively), which are connected on the right side of the figure to lower pole piece 11, known as P1. On the left side of the figure, P1 and P2 are seen to be separated by a layer of non-magnetic material 15 so that most of the magnetic flux generated by the flat coil passes across gap 19 where fringing fields extending out for a short distance are still powerful enough to magnetize a small portion of recoding medium 18
It can be seen that where P1 and P2 face each other their cross-sectional areas have been reduced so as to further concentrate the magnetic flux at 19. In the case of P1 this has been achieved by the introduction of an area of non-magnetic material 111, generally referred to as step P1. In FIG. 2 we illustrate the prior art process that has been used till now to form step P1. Given substrate 22 on which layer 21 (P1) rests, a trench 25 was formed in P1 and then overfilled with non-magnetic material 23. Excess material 23 was then removed by means of chemical-mechanical polishing (CMP) so that the trench ended up being just filled as 111, thereby forming step P1 as shown in FIG. 3.
In the interests of product reproducibility, it is important that the thickness of step P1 be closely controlled and that the entire surface of layer 21 be uniformly planar. lf it is not, any unevenness in the topology will be transmitted to subsequent layers, including the lower portions of P2. Furthermore, as write heads continue to shrink, so will the thickness of step P1, making control ever more difficult.
While being an extremely useful tool for planarizing surfaces that are made up of several different materials, CMP is subject to problems of dishing at heterogeneous interfaces and, additionally, it is usually necessary to over-polish in order to achieve full planarization. The extent of this over-polish is difficult to control, making the final thickness of 111 likewise difficult to control.
The present invention is directed towards solving the problem of how to form step P1 with tight control of thickness and no loss of planarity to the upper surface of P1
A routine search of the prior art was performed. The following references of interest were found: In U.S. Pat. No. 5,805,391, Chang et al. show a stitched head process by IBM while in U.S. Pat. No. 5,282,308, Chen et al. (also IBM) disclose a stitched head planarization process. In U.S. Pat. No. 5,325,254, Cooperrider shows a thin film inductive transducer having improved yoke and pole tip structure.
It has been an object of the present invention to provide a process for filling a trench without disturbing the surrounding surface.
Another object of the invention has been to provide a process for forming step P1 in a read head.
A further object has been that said process provide better process tolerance than CMP.
These objects have been achieved by using a liftoff mask for both the trench formation and the filling processes. As a result of this approach, the area surrounding the trench is not disturbed, the trench depth is not reduced, and the original overall planarity, prior to etching and filling, is maintained.